Nag

nag
verb, transitive. To annoy or irritate someone with persistent fault-finding or continuous urging. To be persistently painful, troublesome, or worrying to, as in “a nagging pain.”

He locked the car, then hurried down the street, pelted by rain. He was distracted; unable to ignore an uneasiness that nagged him. It convinced him that he had forgotten to do something important. The omission would be serious--he just knew it. Probably grounds for termination.

The light over his building’s entryway was burned out. He turned toward the feeble glow of the only streetlamp as he sorted his keys, feeling the dampness soak deeper into his clothes as he stood there, finally locating the door key by feel.

He heard a faint sound as he inserted the key into the lock and began to turn toward it when the blow struck the back of his head. Light flared inside his vision, then he knew no more.

Definitions adapted from The New Oxford American Dictionary, Oxford University Press, Inc., 2005 (eBook Edition, copyright 2008), and from Webster's Seventh New Collegiate Dictionary, G. & C. Merriam Company, Publishers, Springfield, Massachusetts, USA, 1965, depending on which is more convenient to hand.